Water Cycle and Water Insecurity Flashcards
Global Hydrological Cycle
- Closed system
- Inputs = Outputs
2 Processes driving the hydrological cycle
-
Solar Energy:
- Sun heats water
- Evaporation Increases
-Moisture level Increases
- Condensation and precipitation Increase as air cools -
GPE:
-Water moves by gravity
- Runoff and groundwater flow transport water to the sea
Flux
Transfer of water by flows
Annual Flux
Variations in flow due to seasonal and temperature change
Global Stores and Fluxes
- Most freshwater is locked in the cryosphere
Oceans: 97%
Freshwater: 2.5%
Global Water Budget
- Balance between inputs and outputs
- Oceans lose more water than gain
- Land masses gain more than lose
- Residence time in atmosphere is much shorter than oceans
ITCZ- Inter Tropical Convergence Zone
- Air rises and cools due to convectional currents, forming clouds
- Biggest flux, transferring water from oceans to land
Importance of Polar Regions
- Cryosphere locks 66% of freshwater, warm climates release it into the sea
- Polar region contributes to the circulation of heat + water, driving thermohaline circulation
- Polar ocean water sinks (dense and cold)
- Drawing in warm water from above and the tropics
- Water movement from the tropics draw cold water from ocean depths to be warmed again
Fossil Water
- Exploited due to technology
- Aquifiers beneath Kenya hold 70 years worth of freshwater (non-renewable)
Drainage Basin
Area drained by rivers and tributaries (catchment areas) within the watershed- open system. (inputs and outputs can be independent of each other)
3 paths Precipitation follows
Infiltration
Surface Runoff
Evaporation
Precipitation is delayed by :
-Interception by plants/buildings before evaporation or infiltration occurs
- Percolation through rocks as groundwater and subsequent storage in aquifers
Throughflow
Water flow within the soil
Infiltration
Soil Composition:
- Sandy soils have higher infiltration than clay
Previous Precipitation:
- Saturation decreases infiltration (increases surface runoff after heavy rainfall)
Vegetation:
-Root growth can intercept and prevent infiltration
Relief of Land:
-Sloped land encourages runoff, less infiltration
Surface Runoff
Faster flow where gradient is greater, primary transfer is to river
Throughflow
- Clay soil has a high field capacity, smaller pores and a smaller flow rate
- Sandy soils have low field capacity, larger pores, faster flow rates
Percolation
- Flow of water ground/soil to rocks
- Rate dependent on rock fractures and permeability
Groundwater Flow
Flow of water from/through porous due to gravity (slow)
Outputs of Drainage Basins
Evaporation:
- Increases when air is warm, dry and windy
- Larger SA, more evaporation
- Reduced sunlight, less evaporation
- Black absorbs heat, more evaporation
Transpiration:
- Water moves from the plants to the atmosphere, affected by seasons
Stores
Soil Water:
- Water utilised by plants (mid-term)
Groundwater:
- Stored in porous rocks (long-term)
River Channel:
- Stored in river (short-term)
Surface:
- Stored in puddles, ponds and rivers (variable)
Factors affecting Drainage Basin
Climate:
- Influences rainfall and vegetation growth
Soil Composition:
- Influences infiltration rate and throughflow
Vegetation:
- Affects interception, overland flow
Geology:
- Affects percolation and groundwater flow
Relief:
- Steeper gradient encourages faster surface runoff
Deforestation
- Less vegetation, less interception, less infiltration, more flooding, cycle fastens
Land-use change
-Infiltration 5x faster in forests than in grasslands
- Converting to farmlands decreases interception and increases surface runoff
Ground-water abstraction
- Water taken out faster than recharged decreases groundwater flow
e.g. China, groundwater irrigates 40% of farmland, 70% drinking comes from ground water
Irrigation
- High water usage = drop in water table
e.g. Arai Sea Khazikastan, shrink due to farmers using water to grow cotton
Reservoirs
- Delays flows, removes water from the basin
- More water is evaporated from reservoirs globally than used
Convectional Rainfall
- Occurs daily
- Morning heat warms ground, moisture evaporates and rises, as more accumulates it rains
e.g. in tropical climates convectional rainfall is most common
Frontal / Cyclonic Rainfall
- 2 air masses meet
- Wedge can occur of hot air within cold air- depression
At front moist air rises above cold , causing cyclonic precipitation, approx. 100 depressions a year in UK